The light intensity distribution of laser light output from a laser light source has a Gaussian form. A beam intensity conversion optical system which converts the light intensity distribution of laser light from the Gaussian form into to a flat-top form has been in consideration. According to the beam intensity distribution with a flat-top form of the present disclosure, the changing range of the light intensity distribution in a desired region of laser light is equal to or smaller than 10% of a peak intensity.
A laser excitation light source is an example that uses a beam intensity conversion optical system. The laser excitation light source applies the laser light emitted from the beam intensity conversion optical system onto a phosphor to excite white light. The beam intensity conversion optical system converts the light intensity distribution of laser light emitted from the laser light source from the Gaussian form into a flat-top form, and then applies the laser light to a phosphor. That is, the laser light applied to the phosphor has light intensity distribution with a flat-top form so as to suppress convergence of light intensity onto the phosphor.
A conventional beam intensity conversion optical system includes a collimator lens, a lens array, and an objective lens disposed in this order in a direction from the laser light source toward the phosphor. The collimator lens converts diverging light emitted from the laser light source into collimated light. The lens array converts the light intensity distribution of the laser light from the Gaussian form into a flat-top form. The condenser lens applies the laser light passed through the lens array onto an irradiation region of the phosphor.
PTL 1 is known as prior-art technique relating to the present disclosure.